This invention relates to optical scanners in general and more specifically to a light path for directing light from an illuminated scanning area on an object being scanned to a photodetector.
Optical scanners are well-known in the art and produce machine-readable data which are representative of a scanned object, e.g. a page of printed text. Most optical scanners employ line-focus systems in which light from an illuminated scan line on the object is imaged by a lens onto a linear photosensor array or detector positioned remotely from the object. The linear photosensor array is typically a single dimension array of photoelements that correspond to small area locations along the illuminated scan line. These small area locations are commonly referred to as "picture elements" or "pixels." Each photoelement produces a data signal that is representative of the intensity of light from the corresponding pixel. The data signals from the photoelements are received and processed by an appropriate data processing system which may subsequently store the data on a suitable medium or generate a display signal therefrom for reproducing an image of the object with a display device such as a CRT or a printer.
Optical scanners and various components thereof are disclosed in U.S. Pat. Nos. 4,926,041 for OPTICAL SCANNER of David Wayne Boyd; 4,709,144 for COLOR IMAGER UTILIZING NOVEL TRICHROMATIC BEAM SPLITTER AND PHOTOSENSOR of Kent J. Vincent; 4,870,268 for COLOR COMBINER AND SEPARATOR AND IMPLEMENTATIONS of Kent J. Vincent and Hans D. Neuman; and 5,038,028 for OPTICAL SCANNER APERTURE AND LIGHT SOURCE ASSEMBLY of Boyd, et al.; and U.S. patent application Ser. No. 07/906,144 filed Jun. 29, 1992, now U.S. Pat. No. 5,227,620 for APPARATUS FOR ASSEMBLING COMPONENTS OF COLOR OPTICAL SCANNERS of Elder, et al., which are each hereby specifically incorporated by reference for all that is disclosed therein.
A hand-held optical scanner is an optical scanner which is moved across a scanned object, e.g. a page of text, by hand. Such hand-held optical scanners or hand scanners are also well-known in the art and various components thereof are disclosed in U.S. patent application Ser. No. 08/271,404 for Hand-Held Optical Scanner with Speed Control of McConica, et al. and U.S. patent application Ser. No. 08/271,312 for Optical Wave Guide for Hand-Held Scanner of McConica, et al., both of which are filed concurrently herewith, and the disclosures of which are each hereby specifically incorporated by reference.
Many of the early hand scanners were powered by an external power source such as a power unit connected to a wall outlet that was in turn connected to the hand scanner by an electrical cable. Such external power sources were usually necessary due to the significant electrical power required to operate the various scanner components. For example, the optical imaging assembly of a scanner typically comprises an illumination source such as an array of light emitting diodes (LEDs) or a fluorescent bulb. The scanner photoelectric conversion assembly (typically a CCD) also requires electrical energy as do the scanner speed detection circuitry and the scanner central processing unit.
As with most electronic devices, improvements in technology have allowed for the development of practical battery powered hand scanners. Of course, a significant advantage of a battery powered hand scanner is that the onboard power source and mass data storage assembly eliminate the need for external power connections or other connecting cables which tether the scanner to a fixed location. Such an arrangement also significantly improves the mobility and potential use applications for such a hand scanner.
While battery powered hand scanners have many advantages, they are still not without their problems. For example, it is difficult to provide a conventional long focus optical system of the kind used in desktop scanners in the very limited space available in a hand scanner. Even where such long focus optical systems have been utilized, it has been difficult to align the optical system so that the image of the scan line is properly focused on the linear photosensor array.
Partly in an effort to solve some of the foregoing problems, many hand scanners have resorted to contact image sensors to image the scan line. A common type of contact image sensor includes an elongate light source and photosensor array that are both placed immediately adjacent the scan line. Special short focus lenses are then used to focus an image of the scan line onto the photosensor array. While such contact image sensors have the advantage of providing for a compact installation, they require a relatively expensive full length linear photosensor array. Moreover, the short focus optical system substantially limits the depth of field, which can result in increased scanning errors and, in any event, tends to limit the ability of the scanner to scan certain objects.
Consequently, there remains a need for a hand scanner having the features and performance typically associated with full sized desk top scanners, but in a portable, compact package. Ideally, such a hand scanner should be relatively easy and inexpensive to produce, while at the same time providing an efficient optical system to reduce scanning errors. Additional performance gains could be realized by providing an optical system having a large depth of field. Until the present invention, no such device existed.